FR3022542B1 - MIXTURE FOR CONCRETE RESISTANT TO SULFATIC REACTIONS - Google Patents

Abstract

The invention primarily relates to the use of a bulk water repellent for manufacturing a concrete resistant to internal sulphate reactions and external sulphate attacks. The invention also relates to a blend for the manufacture of concrete comprising cement comprising tricalcium aluminates, aggregates, water, and a bulk water repellent.

Description

Mixture for concrete resistant to sulphate reactions. The invention relates to a concrete mix which allows the latter to withstand chemical attacks such as internal sulphate reactions and external sulphate attacks. The invention also relates to a concrete obtained from such a mixture and to the use of a specific component allowing said concrete to withstand internal sulphate reactions and external sulphate attacks.

Concrete is a composite material obtained by a mixture of cement, aggregates, for example sand and chippings, water and any additives to modify the properties of fresh or hardened concrete.

Among the main causes of deterioration of concrete structures, sulphate reactions lead to an internal swelling of concrete which results in external cracks forming concrete break lines.

Internal Sulfate Reaction, commonly referred to as RSI, affects those parts of the structure that have undergone significant heating of the concrete at a young age. This heating is sometimes explained by the desire to accelerate the construction of structures and formulate concrete faster setting and therefore more exothermic. The internal sulphate reaction occurs when the concrete is in contact with an external water supply, the sulphates involved in the reaction being contained in the concrete and resulting from reactions which will be detailed below. Conversely, the External Sulfate Attack, commonly referred to as ASE, does not involve the sulphates contained in the concrete but sulphates from the external environment. This is particularly the case when the concrete is in contact with waters of various origins containing sulphates, for example waters in contact with the gypsum containing elements of biological decomposition of fertilizers or the chemical industry.

To date, there are no satisfactory solutions for reducing sulphate attacks on concrete.

Known solutions include lowering the temperatures reached when setting concrete. For example, cooling systems with pipes embedded in the mass, in which cold water circulates, the reduction of the thicknesses of the parts, the night casting of the concretes, the cooling of the tops on trucks or the tempering concretes with ice.

Also known are solutions consisting of using components such as slags, fly ash or other additions that act as a partial cement substitute binder. But these components complicate the concrete formulation, pose problems of supply of high cost or aesthetics of the facings (case of fly ash from thermal power plants).

In this context, the present invention aims at a simple formulation of concrete that resists both the internal sulphate reaction and the external sulphate attack. For this purpose, the invention relates first of all to the use of a mass water repellent to manufacture a concrete resistant to internal sulphate reactions and external sulphate attacks. The use of the invention may also include the following optional characteristics considered in isolation or in any possible technical combination: the water-repellent is mixed with at least cement comprising tricalcium aluminates, aggregates and water. the water-repellent comprises at least one compound of the isothiazolinone family. the water-repellent comprises a mixture of benzisothiazolinone and methylisothiazolinone. The invention also relates to a mixture for the manufacture of a concrete which is essentially characterized in that it comprises cement comprising tricalcium aluminates, aggregates, water, and a water-repellent mass.

Advantageously, the water-repellent comprises at least one compound of the isothiazolinone family.

Preferably, the water-repellent comprises a mixture of benzisothiazolinone and methylisothiazolinone. The invention finally relates to a concrete made from a mixture as previously stated. Other characteristics and advantages of the invention will emerge clearly from the description which is given below, by way of indication and in no way limitative, with reference to the appended figures among which: FIG. 1 is a graph comparing the longitudinal deformation of a concrete specimen the composition of which comprises water-repellent mass and a concrete specimen the composition of which does not include any water-repellent when these two specimens are subjected to tests demonstrating the phenomena of Sulfur Reaction Internal, - Figure 2 is a graph comparing the longitudinal deformation of a concrete specimen whose composition comprises of mass water repellent and a concrete specimen whose composition does not include water repellent mass when these two test pieces are subjected to tests demonstrating the phenomena of External Sulfate Attack, - Figure 3 a photograph of a part of a concrete test specimen whose composition does not contain any water repellent and which has been subjected to tests demonstrating the phenomena of External Sulfate Attack, - figure 4 is a photograph of a part of a specimen of concrete whose composition contains water-repellent mass and which has been subjected to tests demonstrating the phenomena of External Sulfate Attack, - Figure 5 is a graph showing the evolution of the crack index for a concrete specimen whose composition comprises water-repellent mass and a concrete specimen whose composition does not include water-repellent mass when these two specimens are subjected to tests putting highlight the phenomena of External Sulfate Attack.

According to the invention, the addition in the formulation of a concrete of a bulk water repellent substantially limits the sulfatic reactions occurring in the concrete during its setting, but also years later.

The sulphate reactions involve the formation of a mineral, ettringite, or calcium trisulfoaluminate (3CaOAl2O3.3CaSO4 (30-32) H2O, which is liable to cause swelling during its formation, this swelling possibly leading to concrete cracking, see its bursting.

There are several types of ettringite. Primary ettringite is formed during the hydration of concrete (reaction 1) by involving tricalcium aluminates of formula (CaOsjsAbCb commonly known as C3A and present in cement, water and sulphates.) Once all the sulphates present in the Concrete reacted with ettringite, the latter converted to monosulfoaluminate by reaction of C3A and formed ettringite.The primary ettringite forming in the matrix of fresh concrete malleable, it is not harmful for concrete structures (1) C3A + sulfates + H2O = Ettringite (2) Ettringite + C3A = monosulfoaluminate Secondary ettringite is formed after hardening of the concrete by precipitation dissolution phenomena, especially during an external supply of sulfate where this ettringite may form in the confined spaces of the concrete and may lead to swelling, so secondary ettringite is a result of the Sulfatik Attack phenomenon. External: Delayed ettringitis is formed as follows.

During setting of the concrete, at temperatures above 65 ° C, ettringite is not stable. Reaction 3 below will occur instead of the formation reaction 1 of primary ettringite. So there are still free sulphates in the concrete that will be absorbed by hydrated calcium silicates that will, over the years, gradually release these free sulphates. (3) C3A + sulfates + H2O = Ettringite + free sulfates

In case of infiltration of water into the concrete, free sulphates may react with C3A and / or monosulfoaluminates (Reaction 4) and form delayed ettringite in confined media of the cured matrix. (4) C3A + free sulfates + H2O = Ettringite Delayed ettringite results from the phenomenon of Internal Sulfate Reaction. From a morphological point of view, primary ettringite is generally in the form of micron-sized needles, secondary ettringite may be in the form of needles when it has sufficient space or in massive form in confined spaces, and delayed ettringite is usually in massive form since it is formed almost exclusively in confined spaces.

In a confined environment, the ettringite crystallization pressure rises to 350 MPa which, combined with the increase in volume, causes expansion and cracking of the concrete.

Waterproofing agents are known as mixing admixture to increase the tightness of concretes in which they are incorporated (casings for example).

It has been discovered in the context of the invention that a mass water repellent may be diverted from its known use to limit the formation of expansive ettringite resulting from the Internal Sulfur Reactions and the External Sulfate Attacks. For this purpose, the mass water repellent will notably form bonds with C3A thus limiting the interaction of C3A with water, which prevents reactions (3) and (4) from occurring. The formation of delayed ettringite will thus be limited since external water supply is one of the predominant factors responsible for the formation of this type of ettringite by the Internal Sulfate Reaction. And the formation of expansive secondary ettringite will also be limited since the sulphates will penetrate more difficultly into the concrete, External Sulfate Attack reactions will not occur.

Tests have been carried out on concrete specimens whose formulation comprises a bulk water repellant, in comparison with specimens whose formulation does not include a mass water-repellent, and for environmental conditions favorable respectively to the Internal Sulphate Reaction and at the External Sulfate Attack. The mass water repellent used is liquid and comprises benzisothiazolinone of the isothiazolinone family in a proportion of between 0.01 and 1% by volume. The water-repellent may also comprise methylisothiazolinone, also of the isothiazolinone family, in a volume content of less than 0.01%.

Test No. 1: Internal Sulfate Reaction

This test makes it possible to measure the reactivity of the concrete specimens with respect to the Internal Sulfate Reaction. Three test tubes without water repellent and three test pieces with water repellent were tested.

The formulation of the tested concrete comprises 408 kg of cement (to increase the exotherm) including tricalcium aluminates, 761 kg of sand, 938 kg of washed gravel and 144 kg of water. For specimens containing water-repellent mass, the latter is added in the formulation to the height of 6 kg, or 1.5% of the total mass of the cement.

All the specimens are subjected to a heat treatment simulating a high heating when setting the concrete higher than 60 ° C, this heating being responsible for the formation of delayed ettringite.

To do this, the test pieces are placed in a climatic chamber for 24 hours at a temperature of 800 ° C. and under water conditions close to saturation.

Then the specimens undergo a 7-day cycle at 38 ° C in an atmosphere with a relative humidity of less than 30 ° C, followed by a 7-day cycle at 20 ° C in water.

The three test tubes without water repellent and the three test tubes with water repellent are then placed in two different tanks for 66 weeks.

Measurements of the mass and longitudinal deformations are made from the end of the heat treatment. Longitudinal deformation measurements are made using a gallstone refractometer on the four faces of each test piece. At the end of 66 weeks, non-water-repellent concrete specimens and mass-proofed concrete specimens showed a slight increase in mass less than 5%.

With reference to FIG. 1, after 66 weeks, the longitudinal deformation of the water-repellent concrete specimens whose average is represented by the curve 1 is 0.30%, whereas the longitudinal deformation of the concrete specimens with water-repellent of which the average is represented by the curve 2 is almost zero.

As a result, concrete specimens with water repellency show negligible deformation, whereas the specimens with water repellency have inflated linearly.

These results show that the test tubes without water repellency are reactive with respect to the Internal Sulfate Reaction, which is not the case for non-water-repellent test pieces, which validates the choice of the reactive concrete formula for the Internal Sulfate Reaction. .

Test No. 2: External Sulfate Attack

The test pieces used are those having undergone test n ° 1.

Two months after the completion of the Internal Sulfate Reaction tests, sulphates are added to the water tanks. Are tested a test tube without water repellent and a test tube with water repellent.

The sulphate used is anhydrous sodium sulphate which causes the formation of expansive secondary ettringite. The sulphates are introduced into the water tanks until saturation of the solution is at a concentration of 160 grams per liter at 20 ° C, which corresponds to a concentration approximately 50 times greater than that of seawater .

Measurements of the mass and longitudinal deformations are carried out from the end of the heat treatment and this during 3 months and a half. At the end of the 3 and a half months of testing, the mass of the specimen in water repellent increased by 2.5% while the mass of the specimen with water repellent remained stable.

Referring to Figure 2 having a curve 3 representing the average of the deformation test specimens without water repellent and a curve 4 representing the average of the deformation of the specimens with water repellent.

During the first test month, the deformation of the specimen without water repellency increases significantly by 0.08%, then the specimen deforms more significantly until a deformation of 2% at the end of the test. .

As for the specimen with water repellant, no deformation was observed during the first month, then a significant deformation of 0.08% at the end of the test. At the end of the test, the deformation of the specimen without water repellency is 20 times greater than that of the specimen with water repellent.

A visual examination is also performed during the test.

Figure 3 illustrates a portion of the specimen without water repellant 5 at the 9th week. Significant cracks appear 6. For this test tube, the first cracks appeared during the first week.

For the specimen with water repellent, the first cracks appear at the end of the 10th week of testing. These cracks are much smaller than those observed on the specimen without water repellent. FIG. 4 illustrates a portion of the specimen with water repellant 7 at the 14th week, on which there is the presence of slight cracks 8.

These observations are corroborated by the measurement of the IF cracking index making it possible to quantify the cracking state of the concrete. This index makes it possible to follow the evolution of the damage of the concrete by comparison of the state of cracking at different times. These measurements are made using a fissurometer on the specimens which have surface cracks. Measurements are made according to four axes. For each axis, the number and the opening of each crack that crosses the axis are reported. The crack index is then calculated from these data.

With reference to FIG. 5, the evolution of curve 9 illustrating the cracking index for the test specimen without water repellant shows that this cracking index increases over time to reach a value of 8.7, whereas that for the specimen with water repellent that begins to crack at the 10th week, its cracking index increases slightly to reach a value of about 1 at the end of the test.

Thus, the test piece without water repellant has undergone a significant increase in its deformation, while the specimen with water repellent has undergone a very small increase in its deformation.

Furthermore, the deformation is very strong on the specimen without water repellant, and very low on the specimen with water repellent.

It has thus been demonstrated that the addition of water-repellent in the concrete formulation significantly reduces the degradation of the specimens subjected to an External Sulfate Attack and an Internal Sulfate Reaction. The mass water repellent thus has an inhibiting effect vis-à-vis the internal Sulfate Reaction and External Sulfate Attack. The invention is applicable in the railway field, particularly for the construction of all concrete structures such as bridges, viaducts, stations and tunnels. The invention is also applicable in any construction of civil engineering concrete or building.

Claims (7)

MODIFIED CLAIMS 1. Use of a mass water repellent to make a concrete resistant to internal sulphate reactions and external sulphate attacks. 2. Use according to claim 1, characterized in that the water repellent is mixed with at least cement comprising tricalcium aluminates, aggregates and water. 3. Use according to any one of claims 1 to 2, characterized in that the water-repellent comprises at least one compound of the isothiazolinone family. 4. Use according to claim 3, characterized in that the water-repellent comprises a mixture of benzisothiazolinone and methylisothiazolinone. 5. Mixture for the manufacture of a concrete characterized in that it comprises cement comprising tricalcium aluminates, aggregates, water, and a mass water repellent comprising at least one compound of the isothiazolinone family. 6. Mixture according to claim 5, characterized in that the water-repellent comprises a mixture of benzisothiazolinone and methylisothiazolinone. 7. Concrete made from a mixture according to any one of claims 5 and 6.